We introduced a laser-based noncontact shallow water depth measurement technique from a flying unmanned aerial vehicle (UAV). The water depth is measured by imaging two laser beam spots scattered from the surface and bottom of the water. The effect of water surface waves and UAV tilt angles to the depth measurement has been studied for practical applications. We have further developed this laser-based detection system consisting of a green laser, a global positioning system, a camera with a narrow field of view lens, a laser range finder, and a single-board computer. The measurement system onboard of a UAV flying over a small lake has demonstrated satisfactory water depth measurement capability. The low-cost light weight UAV-based water depth measurement should benefit water depth monitoring, mapping, and reporting in a hazardous environment offering flexibility, mobility, and remote control safe operation.
Planar concave grating wavelength demultiplexers with a flattened spectral response are realized based on SU-8 polymer waveguides. The flattened spectral response is accomplished by using an optimized multimode interference (MMI) coupler as the input aperture of the planar waveguide for all spectrally separated channels. The mode field distribution at the input of the planar waveguide is controlled by adjusting the width of the input taper connected to the MMI coupler. The devices are fabricated by cost-effective one-step UV lithography. Experimental results show that the desired flattened spectral response has been realized. The on-chip loss, crosstalk, and nonuniformity of the fabricated device are −14.8, −22, and 2.5 dB, respectively.
We report on improving lateral resolution of optical coherence tomography (OCT) for imaging of skins using multiframe superresolution technique. Through introduction of suitable slight transverse positional shifts among a series of C-scans, the superresolution processing of the lateral low resolution images at each axial depth reconstructs a high resolution image. Superresolution processing of all depth layers yields a high resolution 3D image. Using known resolution photomasks, 3 times lateral resolution improvement has been confirmed for both low and high numerical aperture OCT imaging. The superresolution processed OCT 3D skin image provides much more feature details for all subsurface depth layers within the OCT axial imaging range.
A 4-channel planar concave grating device with a flattened spectral response based on SU-8 polymer is presented.
The flattened spectral response is accomplished by using an optimized multi-mode interference coupler as the input
aperture of the device for spectrally separated channels. The mode field distribution in the input plane is controlled
by adjusting the width of input taper coupled to the multi-mode interference coupler. The effects of the input taper
width on the flattened spectral response are demonstrated in detail through simulation results. The devices are
realized by using an SU-8 polymer strip waveguide with a UV lithography technology. Experimental results show
that the flattened spectral response can be easily controlled by adjusting the taper width.
Multi-frame superresolution technique has been used to improve the lateral resolution of spectral domain optical coherence tomography (SD-OCT) for imaging of 3D microstructures. By adjusting the voltages applied to 𝑥 and 𝑦 galvanometer scanners in the measurement arm, small lateral imaging positional shifts have been introduced among different C-scans. Utilizing the extracted 𝑥-𝑦 plane en face image frames from these specially offset C-scan image sets at the same axial position, we have reconstructed the lateral high resolution image by the efficient multi-frame superresolution technique. To further improve the image quality, we applied the latest K-SVD and bilateral total variation denoising algorithms to the raw SD-OCT lateral images before and along with the superresolution processing, respectively. The performance of the SD-OCT of improved lateral resolution is demonstrated by 3D imaging a microstructure fabricated by photolithography and a double-layer microfluidic device.
We demonstrate that a 2D eight-fold photonic quasi-crystal (PQC) can be produced by a specially designed prism
via single-exposure holographic lithography. Compared with traditional eight beams in half space for eight-fold
quasi-crystal, we only use 5 beams in ¼ space. From group theory and computer simulation, we have verified the
feasibility of the particular configuration and observed the simulated patterns. Experimental results observed under
SEM agree well with the expectation, confirming that the specially designed prism can be used to fabricate eight-fold
photonic quasi-crystal. This prism-assisted holographic lithography using less exposure beams may benefit
mass production of complex quasi-structures.
We demonstrate that large area eight-fold symmetric polymeric photonic quasi-crystals can be created by a specifically
configured prism via single-exposure holographic lithography. The prism splits an expanded laser beam into five beams
and in sequence converge onto a photoresist with a designed incident angle for forming an interference pattern with
eight-fold quasi-period. Different from a conventional eight-fold symmetry prism, only five continuous surfaces are used.
From group theory, we have verified the feasibility of the particular configuration. And numerical simulations have
confirmed that the eight-fold symmetric periodicity can be obtained. Experimental results with the same five beam
configuration are in good agreement with the theoretical prediction. The kind of specially designed prism may benefit
mass production of large area photonic quasi-crystals by holographic lithography technique.